Spring Vale Electrical Controls (Part 2)

Part 1 of this series introduced the drawings detailing the electrical controls at Spring Vale Sidings Box. There's a brief description of this signal box here. It's helpful to keep in mind the layout, shown below. Clicking on any diagram gives an enlarged image which can be downloaded or printed.

In this instalment we'll look at Block Control on the Up and Down Lines (shown on sheet 2 of the drawing set).

Introduction to Block Control:

Early block instruments were purely communication devices. The safe working of trains depended upon the signalman only giving 'Line Clear' for a train to approach when it was safe to do so. Various improvements were introduced, like 'Sykes Lock and Block' and 'Interlocking Block' but these were partially mechanical systems, not completely foolproof and were not universally adopted. Over the years, successive accidents revealed weaknesses which could be guarded against by adding electrical controls.

Signal Proving:

One source of accidents was trains running away because signals were not displaying a 'Stop' aspect when required, either through a Signalman's direct error or because the position of the signal arm did not correspond with the position of the controlling lever in the signal box. At night (or in conditions of low visibility) a signal lamp 'out' could similarly result in running away.

Normally, 'Line Clear' was given to the box in rear before permission had been obtained for the train to proceed into the section ahead. This was perfectly safe provided that the Home signal was at danger so as to stop the approaching train. In addition, the Distant signal should be at Caution, as advance warning to the driver of the need to stop at the Home signal.

Let's summarise the electrical interlocks required:-

(1) Prove signal arms 'on': The mechanical interlocking on the lever frame responds to the position of the lever - there is no information about the actual position of the signal arm controlled from the lever.

(2) Prove Home signal lever 'Normal' and electric lever lock not energised: This ensures that the Home signal levers are correctly Normal at the time 'Line Clear' is given to the box in rear.

At Spring Vale, Block Control was provided on both the Catchems Corner and Deepfields block instruments to ensure that the relevant Home and Distant signals were 'On' before 'Line Clear' could be given to the box in the rear. The detailed circuit is described below.

Catchems Corner direction:

On the Up Main, the criteria for accepting a train offered from the Catchems Corner direction were:-

- Up Distant Signal Arms (19a/19b) proved 'On'.

- Up Home Signal Arms (levers 20 & 23) proved 'On'.

- Up Home Signal Levers (20 & 23) proved 'Normal' and electrically locked.

On the right of the diagram above is the block instrument to Catchems Corner with two polarised galvanometers and the commutator switch. The right hand side of each galvanometer connects to line and thence to the block instrument in the Catchems Corner direction via contacts on the Block Switch ('BNC'). The Block Switch contacts are closed when Spring Vale Sidings box is 'Open'. On the Up Main, separate batteries are provided for giving 'Line Clear' and 'Train on Line'. Negative 'Line Clear' battery is fed via contacts: '20LCC' (Lock Proving Contact on 20 lever lock, proving lever normal and lock not energised), '23LCC' (Lock Proving Contact on 23 lever lock, proving lever normal and lock not energised), '20RGCR' (contact on Red Signal Proving Relay for signal 20), '23RGCR' (contact on Red Signal Proving Relay for signal 23),'19YCR' (contact on Yellow Signal Proving Relay for signals 19) to the 'LC' pole of the commutator. If the control conditions are met when the signalman places the Block Instrument Commutator to 'Line Clear', current flows from the battery, through the proving contacts, through the commutator at 'Line Clear', through the closed front contact of relay 'T1TPS' (track Circuit 1 Track Repeating Stick Relay), through the coil of polarised relay 'UP MAIN BS' (Block Stick Relay) and via a current limiting resistor to the positive of the 'Line Clear' battery 'RET'. A stick relay is one which, once operated, self-maintains. The 'UP MAIN BS' contact shorts out the chain of proving contacts, allowing the signalman to obtain 'Line Clear' from the box in advance and clear his signals, without losing the 'Line Clear' to the box in rear.

Can we come back to a proper discussion of 'T1TPS' in a later installment? For now, assume that track circuit T1 (the Up Main 'Berth' track circuit) is clear and that 'T1TPS' is energised.

Note, in passing, that the 'DN MAIN BCR' (Block Proving Relay) is a polarised relay which will energise only when 'Line Clear' polarity is being received from Catchems Corner direction. Energisation of this relay is used to release the down signals at Spring Vale Sidings.

Deepfields direction:

On the Down Main, the criteria for accepting a train from Deepfields direction were:-

- Down Distant Signal Arms (37, 36a/36b) proved 'On'.

- Down Home Signal Lever (35) proved 'Normal' and electrically locked.

Similarly, on the right of the diagram above is the block instrument to Deepfields. On the Down Main, separate batteries are provided for giving 'Line Clear' and 'Train on Line'. Negative 'Line Clear' battery is fed via contacts: '35LCC' (Lock Proving Contact on 35 lever lock, proving lever normal and lock not energised), '36a/b YCR' (contact on Yellow Signal Proving Relay for signals 36a/36b), '37YCR' (contact on Yellow Signal Proving Relay for signal 37) to the 'LC' pole of the commutator. If the control conditions are met when the signalman places the Block Instrument Commutator to 'Line Clear', current flows from the battery, through the proving contacts, through the coil of a polarised relay 'DOWN MAIN BS' (Block Stick Relay) and via a current limiting resistor to the positive of the 'Line Clear' battery 'RET'. The 'DOWN MAIN BS' contact shorts out the chain of proving contacts, allowing the signalman to obtain 'Line Clear' from the box in advance and clear his signals, without losing the 'Line Clear' to the box in rear.

Note, in passing, that the 'DN MAIN BCR' (Block Proving Relay) is a polarised relay which will energise only when 'Line Clear' polarity is being received from Deepfields direction. Energisation of this relay is used to release the Up signals at Spring Vale Sidings.

In the next instalment, we'll talk about Lever Locks.

Princes End Electrical Controls (Part 2)

Part 1 of this series introduced the drawings detailing the electrical controls at Princes End after it became a Fringe Box to Wolverhampton Power Signal Box. There's a brief description of this signal box here. It's helpful to keep in mind the track layout, shown below.

This simplified and approximate diagram shows Princes End with the single line to Wednesbury on the left and the double track to Tipton Curve Junction (controlled by Wolverhampton PSB) on the right. Clicking on any diagram displays a higher-resolution version which can be downloaded or printed

Layout of Relay Room

Layout of relay room at Princes End

All the relay rooms on the West Midlands Resignalling were more-or-less the same size - they certainly all followed the same basic design. Whereas some of the main-line relay rooms were packed with equipment, there was plenty of spare space at Princes End, with cable terminations on one long wall, battery chargers on the other long wall and equipment in the middle of the room.

Cable Terminations

One long wall was dedicated to cable terminations for signalling, telecommunications and power cables. All cables entered the relay room underground from the concrete trough cable route outside. The signalling cables were terminated on substantial test disconnection links to facilitate tracking down faults. The other side of the disconnection links was wired via overhead cable trays to the equipment. Cables PE1 and PE6 both ran to Location Case PE2/1. Cable PE2 ran to Location Case PE2/2. Cables L1 and L2 ran to the signal box. Finally, track circuits 464 and 467 had their adjustment resistors (464TO and 467TO), fusing and links mounted on the termination panel.

Layout of Cable Termination Panels at Princes End

Relay Racks at main line relay rooms

The West Midland Resignalling introduced 'Geographical Interlocking' using pre-wired relay units each dealing with a standard signalling function such as a 'Main Signal' or a 'Single Ended Point'. These standard units were then interconnected by multicore cables plugged into plug couplers, allowing rapid replacement during fault-finding. Relay racks mounting the 'Geographical' units were normally in one or more rows away from the walls giving technicians access to both the front and rear of the racks.

Relay Rack at Princes End

Princes End was a much simpler proposition, with only a few relays to be accommodated, so the relay rack was 'free-wired' (as all relay interlockings had been prior to the adoption of 'Geographical' units). Next to the relay rack, the Standard Telephones and Cables Train Describer was housed in an equipment cubicle with hinged access doors.

Layout of relay rack at Princes End

The relays were mainly Westinghouse style 'P'. This series of miniature plug-in railway signalling relays was the immediate predecessor to the 'BR930' plug in relays still used today.

The top row of relays were for signal and miscellaneous relays. The Down colour-light starter (lever 6) needed 3 relays, plus 1 relay associated with the next signal (WN186, controlled by Wolverhampton). The Up Home 1 (lever 19) needed 6 relays. There were 4 style 'J' relays for miscellaneous functions. The second row of relays mounted 11 relays associated with track circuits. The remaining rows were unused, apart from two style 'R4' Track Feed Sets for track circuits 464 and 467.

Power

A secure Signalling Supply of 650 volts a.c. was fed throughout the area to power Location Cases and Relay Rooms. The relay room at Princes End had a 1 kVa step-down transformer to 110 volts a.c. which was distributed to various power supplies, low voltage transformers and battery chargers. The diagram below shows two 50 volt d.c. supplies, two 12 volt d.c. supplies (one with battery back-up), 12 volts a.c. (for the lamps on the illuminated diagram at Princes End) and 110 volt a.c. supplies.

Note the way in which supplies were designated. 'B' identified the positive and 'N' the negative. The nominal voltage was appended, for example 'B12' meant 12 volts positive Where there were multiple supplies with the same nominal voltage, suffixes were added such as 'N50(S)'. Alternating supplies had an 'X' added such as 'BX110'.

Power Supply Layout

The Fuse Panel for all the supplies was located on the end of the relay rack. Layout and Allocation of Fuses

In the next instalment (here), we'll tackle some of the relay circuits.